My accelerator linkage has always had an awful lot of "free play" in it. I can press the accelerator pedal down at least one inch without raising the RPM level of the engine above idle. Although lots of linkage rods are moving, it appears none of them are actually doing anything. At about 1 inch of downward movement on the accelerator pedal, the rod to the injection pump (I believe) starts to move and the RPMs increase and the engine revs up fine. The car starts and runs fine--has "good" pickup for a diesel and I'm perfectly happy with city and highway performance.

However, I would like to get quicker throttle response to movement of the accelerator pedal. It appears to me that adjusting the various linkage rods could help, but I'm concerned with the size of adjustment necessary. The car has never had any serious work (205K miles) and it doesn't seem plausible that normal wear and tear could cause this excessive slop. Before I do something foolish, can anyone tell me if this kind of "sloppy linkage" is by design and should be left alone?

I see a single threaded rod near the firewall where the main linkage originates. I am tempted to take up slack there, so I won't have to fool with the multiple linkage rods on top of the valve cover. That would be easy to undo if for some reason it adversely affected performance. Anybody have any suggestions or cautions? Thanks, John Downey

I am not familiar with the details of the 1985 300SD throttle linkage, but I have a 1982 240D that suffered a similar problem. On that car the throttle movement from the pedal, essentially linear motion, is converted to a rotating motion via some levers and transmitted to the set of rods that actually connects to and controls the injection pump fuel delivery set up. This is mechanically complex to describe, but when it is in front of you it is relatively straight forward.

The mechanical connection that sort of hangs off the bracket supported from the valve cover is where the problem occurs. The rod delivering the torque to the set of levers to move the throttle control rod up and down is connected to the levers via a set of male and female plates. The male plate has two prongs and an extension of the rod that engage appropriate holes/slots in the female plate. The male plate is covered in a rubber material bonded to the prongs and face of the plate. On my car the rubber bond failed and the rubber subsequently fell off. It was around a quarter of an inch thick, which made the first inch or two of pedal travel do nothing. It also limited the top speed, but had no effect on starting or normal running. My daughter never really noticed this and when she came home from college one day, I drove the car and thought it was dead. Upon inspection I found the problem. It was a weekend and no parts were available so I used electrical tape and popsicle sticks to take up the slack. That has worked for two years now.

Like I said at the beginning, your throttle linkage might be different, and all my rambling is just an anecdote, but it is the best I can do from here. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Jim: Thanks for the reply. Your description of the linkage connection sounds similar to mine. The bracket on top of the valve cover may very well be hiding the problem. I couldn't inspect it very well today, because it was obscured with about a pound of grease (looks like it was literally ladled on). I will clean it and inspect it more closely. That would explain how the adjustment could be so far off...thks again. John Downey